Noise figure calculation

[abhijitrc]

How to determine the combined noise temperature of the front end ( analytically) at the output of the IF stage.????

 

[BigBoss]

If you know Noise Temperature and Gain of each stage, use Friis formulae for both Noise Figure and Noise Temperature

 

[jiripolivka]

How to determine the combined noise temperature of the front end ( analytically) at the output of the IF stage.????

Receiver noise figure is referred to receiver input. At IF input the noise power is greater by the gain of LNA and down converter. If those elements are linear, noise power will not change receiver noise figure.

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If you need the noise temperatures instead of noise figure, as P=kTB, noise power P is equivalent to the noise temperature.

 

[volker_muehlhaus]

"Cascaded noise figure" online calculator:

https://www.changpuak.ch/electronics/calc_01.php
**broken link removed**

 

[abhijitrc]

what is the overall effect of LO ( AM noise/ phase noise) on the receiver noise temperature ? how it effect the receiver performance.!!!!

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In FM based superhetrodyne receiver how phase noise plays a role in its sensitivity.

How sensitivity is related to noise figure??

 

[jiripolivka]

LO effect depends on the "purity" of the signal source. Good signal generators allow to achieve a low receiver noise temperature. For example, in microwave region, Gunn oscillators and DROs are "clean" and good to use in low-noise receivers. Phase noise has nothing to do with thermal noise and does not affect receiver noise temperature.
In mm-wave region, frequency multipliers are used to generate LO signals from lower-frequency sources. I often observed that receiver noise temperature grew due to the use of wideband MMIC amplifiers in the LO chain. Those amplifiers are wideband, so they amplify also thermal noise in addition to the desired CW signal. The remedy was found in a narrow-band filter before mixer LO input. Simple resonator was found adequate.

 

[Element_115]

How to determine the combined noise temperature of the front end ( analytically) at the output of the IF stage.????

If you are getting the IF(data) out, you might want to do a BER and translate Eb/No to
SNR

https://www.edaboard.com/threads/49446/

Good luck.

 

[tony_lth]

I published a paper about the LO phase noise vs. receiver BER, but it is in chinese.
You can reference AWR example, there is one about phase noise vs. receiver BER. You can start from it.

 

[abhijitrc]

How amplifier noise temperature increases with temperature?

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How amplifier noise temperature increases with temperature?

Sorry for the wrong statement , what i meant to state that "How amplifier noise temperature increases with frequency?"

 

[jiripolivka]

How amplifier noise temperature increases with temperature?

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Sorry for the wrong statement , what i meant to state that "How amplifier noise temperature increases with frequency?"

This is not a general question; it depends upon the amplifier design. You should "tune" the LNA for the lowest noise temperature, and flat over frequency